1. Field of the Invention
The present invention is directed to sensor technology and relates in general to an apparatus for measuring a body fluid circulating a living body and a tissue constituting a circulatory organ.
In particular, the invention relates to a technology for grasping a state of blood in distal end part to carry out an evaluation of health, a diagnosis of a disease, an evaluation of medicines, and the like.
2. Description of the Related Art
Heretofore, for the purpose of carrying out the evaluation of health of a living body, the diagnosis of a disease, the determination of an influence of medicines exerted on a living body, and the like, there have been proposed various methods utilizing information obtained from blood. In terms of a medical treatment for example, there is a method in which the blood is collected from a living body, and the blood concerned is applied to a component analyzer to obtain a circulation information from a rate of the various blood components contained in the blood to thereby evaluate the health state of the living body, and the like.
Here, circulation dynamics means a state in which the blood and a lymph fluid which are moved through the inside of the circulatory organ to supply tissues and cells of a living body with oxygen and nutrition to carry carbon dioxide gas and wastes away vary continuously with time. For example, a blood flow rate, a change in blood flow, a flow property, a pulse wave and the like correspond to the circulation dynamics.
However, this method is not suitable for the case where the circulation dynamics needs to be measured to evaluate the health state of a living body at locations away from medical facilities, and the case where the circulation dynamics needs to be measured to evaluate regularly the health state of the living body with the circulation dynamics measuring apparatus being usually mounted to a living body because when the blood is collected, a living body needs to be pricked with an injection needle. Then, there has been developed an apparatus with which a wave is noninvasively inputted from a surface of a living body into the living body to be reflected by the body fluid flowing through the living body, in particular, the blood, and then, the blood state is analyzed on the basis of the motion and the position to measure the circulation dynamics to thereby evaluate the health state.
On the other hand, as for a prior art of evaluating medically the health evaluation, there is known the method made by Yuji Kikuchi and entitled “Measurement of total blood flowability using a capillary model,” Food Research Result Information (medical journal), No. 11, 1999, i.e., a method in which the blood is collected from a subject and a blood rheology is measured on the basis of a passing time of the blood flow under the constant pressure using a micro-channel array made by a lithographic technique. This method is used, whereby the blood rheology can be measured as the circulation information, and also, the health state can be evaluated on the basis of the resultant value.
In addition, as for a prior art of evaluating noninvasively the health in a home or the like, there is known a method in which a wave such as light is transmitted from a skin surface of a living body to the living body to receive the reflected light to thereby detect the flow rate of the blood flowing through a blood vessel. That is, this method is such that the detected flow rate is differentiated to obtain an acceleration pulse wave as one of the circulation information to thereby evaluate the health state. Here, FIG. 15 is a block diagram showing an internal configuration of a signal processing portion 600 of a conventional circulation information measuring apparatus., and a state of connection between the signal processing portion 600 and a circulation sensor portion 607.
As shown in the figure, the signal processing portion 600 is schematically constituted by a driving portion (light emitting portion) 601, a reception portion (light receiving portion) 602, a signal arithmetic operation portion 603, and an output portion 604. The driving portion (light emitting portion) 601 lights a light emitting element 605 installed in a circulation sensor 607 to transmit a driving energy adapted to apply the light towards a blood vessel. The reception portion (light receiving portion) 602 amplifies a signal which is generated at the time when a photoelectric receiving element 606 installed in the circulation sensor 607 subjects the light applied thereto to the photoelectric conversion. The signal arithmetic operation portion 603 executes a processing program stored in a memory region (not shown) provided therein to execute various processings concerned with the measurement of the circulation information to thereby output the processing results to the output portion 604. Then, the signal arithmetic operation portion 603 converts a level of the received signal into a quantity of change in blood volume, and then, differentiates the resultant value twice to thereby obtain the acceleration pulse wave as the circulation information.
In addition, FIG. 16 is a block diagram showing a configuration of an example of a conventional system for measuring quantitatively the blood flow rate. This system is constituted by a flow rate measuring system 702 and a blood vessel diameter measuring system 701. An ultrasonic wave probe 706 is placed perpendicularly to a blood vessel 705, whereby an ultrasonic wave beam is applied to the blood vessel 705 and a diameter of the blood vessel is measured on the basis of an echo from the wall of the blood vessel, and the blood flow velocity is measured with two other ultrasonic wave probes 707 and 708. The two ultrasonic wave beams are used, whereby the flow rate of the blood can be measured on the basis of the angle between the two ultrasonic wave beams irrespective of the angle between the ultrasonic wave beam and the blood vessel, and the diameter of the blood vessel and the blood velocity which have been measured are processed by a microcomputer 703, and the resultant data is displayed as the blood flow rate on a display device 704.
However, in the blood rheology measuring apparatus using the micro-channel array, since the blood is collected from a subject by any means, his/her elbow portion must be pricked with an injection needle using a syringe to collect the blood. Thus, a subject needs to go to a medical facility or the like for the collection of blood. In addition, in the case where as shown in the prior art, a wave is inputted through a skin surface of a living body into the living body to be reflected by the body fluid flowing through the living body to analyze the blood state from the motion and the position of the reflected wave to thereby obtain the circulation information in order to evaluate the health state of a subject, contraction (strain) and slackness of a blood vessel in a living body (change in diameter of a blood vessel) exerts an influence on a fluid state of the blood in the living body to change the circulation information. Hence, it becomes difficult to measure the circulation information with which an essential health state should be evaluated. In addition, since the fluid state of the blood is also changed due to fluctuation in a blood pressure, when evaluating the circulation dynamics, it is necessary to take a change in blood vessel and blood pressure into consideration.
Moreover, in the conventional blood flow measuring system, it is necessary to use an ultrasonic wave prove for measurement of a diameter of a blood vessel and ultrasonic wave probes for measurement of a blood flow. If independent probes are used, since alignment thereof is difficult to be carried out, it is difficult to measure a diameter of a blood vessel and a blood flow velocity in the same position within a blood vessel, and also, there is a limit to the miniaturization. Further, since the independent probes are used, there is a problem in that since dispersion in sensitivity is difficult to be adjusted for the probes, such probes are unsuitable for mass production, and so forth.
Since in the measurement of the circulation dynamics of a distal end part (e.g., the tip of a finger) of a living body, a measurement area is narrow and a diameter of a blood vessel is also small, in the system as in the prior art in which there is a limit to the miniaturization, there is also a problem in that it is difficult to measure the circulation dynamics of a distal end part of a living body.
Furthermore, since no influence of the blood pressure is taken into consideration, the accurate evaluation is impossible from a viewpoint of the evaluation of the circulation dynamics.
In the light of the foregoing, the present invention has been made in order to solve the above-mentioned problems associated with the prior art, and therefore, the present invention aims at measuring the circulation information with high accuracy irrespective of the degree of strain of a blood vessel of a part to be measured in a living body when a wave is noninvasively inputted through a skin surface of the living body to be reflected by the body fluid flowing through the living body, and then, the state of the blood and the like is analyzed on the basis of the motion and the position of the reflected wave to obtain the circulation information in order to evaluate the health state.
In addition, it is an object of the present invention to provide a circulation dynamics sensor which is capable of measuring the circulation dynamics with accuracy even in a part to be measured having a narrow measurement area and a small blood vessel diameter.